[tex]\displaystyle \left \{ {{4x+y=7} \atop {3x-7y=13}} \right. \\\\\left \{ {{y=7-4x} \atop {3x-7y=13}} \right. \\\\3x-7(7-4x)=13\\x=2\\y=7-4*2\\y=-1\\(x,y)=(2,-1)[/tex]